Surge relief means for conduits



Mwch 9 J. B. COOPER ETAL SURGE' RELIEF MEANSiFOR-. CONDUITS 2Sheets-Sheet 1 Filed Feb. 13, 1939 James E. Cooper I Zhinentors [V0272012 CI Prjca I Gttomeg Patented Mar. 17, 1,942

' UNITED STATE PATENT OFFIC SURGE RELIEF MEANS FOR counmrs ApplicationFebruary 13, 1939, Serial No. 256,256

12 Claims.

The problem of surging within an air conduit,'

inventors herein, Serial No. 216,028, filed June 27,

1938, and to his Patent Nd. 2,208,554, issued July 16, 1940. While theinvention is of especial importance in this particular fieldfit willlikewise be found of importance in any system wherein, due to thepeculiar conditions of generation of pressure and control thereof,surging is likely to arise.

Such surging is an alternate sharp increase of pressure and a sharpdecreaseof pressure within the conduit, thereby producing abrupt surgepeaks of maximum pressure interspersed with valleys of very low ornegative pressure. The blowers employed in such systems are generallycentrifugal blowers or superchargers, and such blowers tend to becomeunstable when the flow therethrough is reduced below a predeterminedvalue or rate. This instability arises from alternate building up andbreaking down of velocityto-pressure-head conversion in the difiuser orconduit, and is characterized by violent air vibrations in the air duct.In any type of installation such violent surging is apt to break theduct, and especially is this true in aircraft installations where theduct must be made of the lightest possible construction suited to normalconditions'in order to save weight. In any event it causes overheatingof the air by turbulence to such an extent that there is danger offailure throughout all parts of the system which are exposed to suchincreased temperatures. The impellers of the aircraft blower orsupercharger, for instance, are sometimes formed of a magnesium alloy,and the heating may be of sufdclent magnitude in a comparatively shortspace of time that these blower impellers may fail, and thesupercharging sys tem may thereby break down and become inoperative,with possible serious consequences, if the airplane is operating at ahigh altitude.

In a typical aircraft cabin air supply or supercharging system, such asis disclosed in the patent and copending application referred to above,the blower normally operates continuously with the engine which drivesit, and that engine would normally be one of the propelling engines ofthe airplane. Sometimes it might be anauxiliary engine which would bedriven in order to supply power for auxiliaries and accessories aboutthe aircraft. In either case the blower is normally operating at alltimes that the aircraft is in flight, and the controls therefor are so"arranged that up to a given altitude, say 8000 feet, the control systemcontrols only the rate of flow through the cabin, and does not operateto produce any supercharging within the cabin. The supercharger, then istaking in air from the surrounding atmosphere, converting velocity intopressure head, and discharging the compressed air within the cabin,whence it is discharged by or through other means and outlets. When itis remembered that the compression of the air tends to heat it, and whenit is remembered that the blower may betaking in air which even up toperhaps 2000' feet or more may be climatically heated to say 90Fahrenheit, it will readily be seen that the air discharged within thecabin may' be uncomfortably warm. While normally means are provided forcooling this air when necessary, such as an intercooler exchanging heatas between the external air and the compressed air in the duct, yet ifthe outside air temperature is high, this intercooler can have butlittle effect to reduce the temperature of the air going into the cabinto a bearable temperature, under such conditions, and it has beenobserved by actual tests that the temperature of the air within thepressure duct may be in the neighborhood of F. during engine cruisingspeed, andwhen the engine to which the supercharger is connected isturning over faster, as when taking ofi or climbing, the temperature ofthe, air in the pressure duct may be considerably greater, 240 F., forexample.

Under any such conditions it will be necessary to close off the pressureduct from the cabin by suitable valve or control means-to prevent thehot air from entering the cabin. This does not operateto the discomfortof passengers, since the cabin willnot normally be supercharged ataltitudes below 8000 feet, and at the latter altitude the surroundingair temperature seldom exceeds the comfortable temperature range, and inany. event the intercooler, normally provided, can I which is related tothe problem of temperature control, is only acute at altitudes belowthat at which supercharging commences.

If we assume .that the temperature of the air entering the cabin fromthe pressure duct is too high to be comfortable, and that the copilot orother attendant has closed off this air supply duct between the blowerand the cabin, or if the normal supply of air to the cabin has beensubstantially throttled, it will be evident at once that the blower nowoperates at such a slow rate of flow that there is alternate building upand breaking down of pressure within the diffuser or duct.Immediately'the surging will commence within the duct, and the presentinvention is particularly designed to provide a means to relieve suchsurging automatically by smoothing outand lessening the peaks thereof,yet by the provision' of means which will not adversely affect thenormal operation of the blower, nor cause loss of pressure under anynormal operating conditions.

It is a further object to provide such surge relief means which will besafeguarded and automatically controlled, not merely by pressure meansbut also or alternatively by thermostatic means, whereby as surgingtends to build up temperature within the duct, the thermostatic meanswill automatically respond and decrease the surging effect, therebykeeping the temperature below a dangerous or undesirable maximum.

It is a further object to provide such surge re-' lief means capable ofincorporating both a pressure control and a thermostatic control, inwhich each reacts with and modifies the operation of the other, for itis important that the device the surge relief means, associatedtherewith in a primary form, and Figure 3 is a similar view illustratinga somewhat more complex but preferred form. Figure 4 is a view similarto Figures 2 and 3,

illustrating a form which is suited to unsupercharged operation.

The outline of the pressure cabin is indicated by the dotted line 9 inFigure 1, and it may be.

percharger or blower I is located outside the supercharged space, andusually is closely coueration to remove the resisting force so that thesurge relief means may operate easily and with a minimum of force, andtherefore with a maximum of responsiveness to surges, when surgingconditions are encountered.

It is a' further object to provide mechanism for the purpose indicated,which-shall be simple ing drawings, described in this specification, and

as will be more particularly defined by the claims which terminate thesame.

In th accompanying drawings we have shown our invention embodied in anillustrative form or forms, and incorporated in a typical aircraft cabinsuperchargi'ng system, all according to our present preferred form andarrangement.

Figure 1 is in general an elevation, and in part a section through aportion of an aircraft cabin supercharging system, illustrating thesurge relief means incorporated therein.

Figure 2 is a section through the air duct and pled to and continuouslydriven by one of the propelling engines of the aircraft. Thepropellingmeans for the blower I is not shown herein,

and any suitable motor means may be employed for driving it. It isillustrated conventionally as a centrifugal blower, taking in air at I0from the surrounding atmosphere, and discharging it through the duct I Iinto the supercharged space,

represented by the cabin 9. Between the blower.

nature of control of these elements is quite immaterial in so far as thepresent invention is concerned, and the elements are illustrated onlydiagrammatically.

- Various controls may be employed to govern the rate of flow ofthe airinto the cabin, or, for high altitude operation, the pressure within thecabin. The details of construction of such mechanism form no essentialpart of the present invention, and as such control mechanismis-disclosed in the patent and copending application of N. C. Pricereferred to above, it is suflicient to note here that such controlmechanism will normally incorporate an inlet valve 2, capable of seatingat 20, or of moving towards or away from the seat at that point, togovern or close oif altogether inflow of air into the cabin from theduct II and through the outlet represented at ll. The valve 2 forautomatic operation is controlled by various devices, which need not bedescribed in detail, but which consist in part of a servo piston 2I,with its hollow stem 22, and the governing piston 23, with its stem 24positioned to follow up and to close or nearly to close the axial borein the stem 22. The piston 23 moves in part in response to a spring 25or similar means, and in part in response to diiferences of pressure atits opposite sides as communicated to it from a source of pressuredifferential, for example through the connections 26 and 21. This sourceof pressure differential may be convenicontrol of an attendant, as by apin 28 connected to a mechanism, that extends to the attendant'sstation. It is by such mechanism as the latter that the valve may beclosed under hot weather conditions, as indicated above, the

manua mechanism 28, 29 over-riding any automatic mechanism, such as thepistons 2I and 22. Naturally when the valve 2 has been thus closed thereno longer exists any pressure differential through the Venturi meter I5,and consequently the pressure within the connections 26 and 21 isequalized. It is equally clear that so long as there is a flow throughthe Venturi meter, at least of appreciable proportiona'there is apressure difference as between theconnections 23 and 21, and that thispressure difierence varies as a function of the rate of flow.

It will alsobe clear, from what has been said above, that when the valve3 is closed, or nearly closed, thus drastically curtailing the normaloutlet for air fromthe blower, and the blower I continues to operate,surging will commence, since there is a building up of pressure head andsudden release of pressure, the duct ll being closed 03 or greatlyrestricted. Accordingly it is in the duct H, between the blower l andthe valve 2, that the surge relief means is installed.

Such surge relief means may at first appear to be merely a valve whichmay be opened upon the imposition thereon of pressures exceeding a givenmaximum; in other words,a mere pressure ,relief valve. It is not,however, since it must be held closed during the occurrence ofrelatively high pressures under normal supercharging conditions, yetmust be disabled and enabled freely to open, or with but littleresistance to opening, .upon the occurrence of surging even at lowpressures. It must open sufliciently readily and sufficiently insynchronism with the surge peaks, that is to say, without appreciablelag, that the surge peaks are in etiect leveled oil, whereas an ordinarypressure relief valve, which merely opened upon the occurrence of apressure in excess of a given maximum and closed upon the reduction ofpressure to or below the maximum, would be unsatisfactory and would failto function properly, if for no other reason, probably because ofexcessive lag, and particularly would this be the case where such apressure relief valve had to be held closed up to fairly high pressuresduring normal operation, and could only open upon the occurrence ofpressures in excess of such normally-to-be-expected pressures.

A simple form of such a valve is shown in within the'duct II, the pin 35has been drawn downwardly to an extent that this pin does not interferewith the full seating of the valve 3 upon its seat 30. When the valve isthus seated, its area exposed to such pressure as exists within the ductII (that area inside of the seat 30) is less than its area which isexposed to such pressure as exists within the chamber 33, for the latterarea is the entire area of the piston-like valve. Since the pin 35 issomewhat withdrawn from the pierce 34 in the piston, the absolutepressure within the closed chamber 33 is substantially equal to thepressure within the duct ll (very slightly less because of leakageoutside the, skirt 32 and out at the .ports 39) The pressures beingsubstantially equal, but the areas Figure 2. The valve 3 seats normallyat 33, in a collar 3| which is secured about an aperture in the duct ii.The valve 3 is formed as a piston, and may be provided with a skirt 32having very slight clearance, by which skirt it is guided for axialmovement within a closed chamber 33. The valve 3 is pierced, and thepierce 34 may be axially disposed, whereby a pin 35 may cooperatetherewith. The pin 35 is slidable axially in a guide 36 in a bracket .31forming part of the collar 3|, or supported from the latter.

Movement of the pin 35 is under the control of a somewhat resilientelement 3, which is a thermostat. One end of this spirally coiledbimetal strip is held in the pin 40, rotatably adjustable within thebracket 31 to vary the initial setting of the thermostat, and itsopposite end is engaged between spaced shoulders or stops 38 upon thepin 35. The bimetal of the thermostat 3 is so arranged that uponincrease of temperature the thermostat tends to push the pin .35upwardly, and upon decrease of temperature the thermostat tends to pullthe pin 35 downwardly. As will be understood, the chamber 33 is providedwith apertures 33, whereby air may escape from the interior of the ductI I upon the raising of the'valve 3 from its seat.

Assuming normal operating temperatures being unequal, there is aresultant downward force which tends to hold the valve 3 seated, andthis is true whatever may he the absolute pressure within the duct, solong as the increase in such pressure is not too rapid to be equalizedthrough the pierce 3E, and so long as the pierce is kept open for suchequalization.

Obviously, if a sudden increase of pressure occurs within the duct,pressure equalization through the pierce 36 can not-occur withcorresponding rapidity, the upward force overcomes the downwardvalve-seating force, the valve' rises, the elastic air volume within thechamber 33 is compressed somewhat, the excessive pressure is relievedby'slight and momentary opening of the valve, and, assisted'byreaction-and expansion of the elastic air volume, the valve reseats. Ifthe increase of pressure continues without surging, andat a rate not toorapid, the pressure will equalize itself as .between the interior of thechamber 33 and the interior of the duct H, and the valve will remainseated. This is not a surge condition-merely an increase of pressure,due, for instance, to an increased rate of operation of the blower.

If, however, the sharp increase of pressure recurs rapidly, and surgingcommences, it is clear that the valve will not reseat before it is againurged away from'its seat by the following surge rise to lift the pin 35through the necessary distance, or because the thermostat is not responsive with suflieient rapidity to a temperature rise, the pressurewithinthe chamber 33,-acting downwardly on the valve, will becomesubstantially equal to the pressure acting upwardly upon the .valve, andnow only the gravity effect will tend to close the valve; the latter isovercome, and the ,valve is held open, so long as surge peaks follow oneanother rapidly. It is clear, then, that the valve will function as asurge relief-valve purely by pressure effect, and without necessaryreliance on temperature effect.

The valve may be thus operated as a surge relief valve primarily oradditionally under the influence of increased temperatures, whatever thecause of the temperature rise, though such increased temperaturesinevitably accompany increased pressures, or sur ing. If the temperaturetends to rise within the duct-with or without an increase in pressure,the pin 35 is moved upwardly until it closes the pierce 34, and nowpressure may not equalize as between the interior of the chamber 33 andthe interior of the duct II. I If there is no increase of pressure, orsurging, nevertheless leakage from the chamber 33 past the skirt 32 andout the ports 39 reduces to open the valve is primarily, it not solely,the

increase of pressure within the duct. 1:! this is a surge condition, thevolume within the chamber 33 will gradually be reduced as the valve 3 isrepeatedly lifted, either by leakage through the pierce 34 past the pin35, as the piston-like valve is repeatedly squeezed upwardly, or byleakage past the skirt 32, which fits with some clearance,

perhaps a thousandth or a. few thousandths or an inch. As the valve isopened, thereiore, the duct is vented to reduce the temperature, or,under surge conditions, the surge peaks are reduced, and the compressedair volume in the chamber 33 tends always to close the valve as thepressure drops, unless restrained by the operation of the thermostat 4through the pin' 35, which is unlikely, as the force of the thermostatis slight. The valve is thus opened wholly'by surge peak pressures, andclosed by an elastic air volume and by gravity, and since it is small inmass, it has little inertia of its own and tends to follow very closely,and substantially without lag, the surge peaks, and to relieve thelatter and smooth out the surges.

As the temperature drops, due probably to elimination of surgeconditions or to relief from surges, the pin 35 moves downwardly,receding from the pierce 34, and again pressure may, equalize as betweenthe interior or the chamber 33 and the interior of the duct II, andgradually the piston 3, in its average position, moves toward closedposition, and if it may close without again inducing surging it will doso automatically It surging has occurred, but hasbeen relieved withoutsuch increase of temperature as to lift the pin 35 to the full extent ofthe upward movement of the valve 3, again pressure may be equalizedthrough the pierce 34, as between the interior of the chamber 33 and theinterior of the duct I I, and again the piston-like valve 3 movesdownwardly until it seats, unless to some extent it may be restrained bythe pin 35 and thermostat 4.

The above provides a surge relief valve which will operatesatisfactorily, but it still requires force to open the valve in excessor the normal pressure which immediately preceded surgin conditions,andwe prefer to provide means to disable the resistance of the valve .toopening, which disabling means will automaticallybecome effectiveimmediately upon the occurrence or such mal flow conditions there is agreater differential of ressure in the latter.

Thus in' Figure 3 the construction of the surge relief valve is similarto that just described with the exception that a vent passage 50 admitsto i tion) extended thereto, whereby it becomes a pressure chamber underthe influence of pressure conditions at the entrance to the Venturimeter l5, and the chamber 52 is connected to the suction connection 21(or other suitable low or minus pressure connection dependent upon rateof flow), whereby it becomes a suction chamber and is, under theinfluence of fiowdnduced suction through the throat of the Venturi meter[5. A

spring 55 also serves to urge the vent valve 5' toward open position,and the force supplied by this spring 55 may be suitably varied by anyknown means.

conditions as might tend to produce s nz- 1 Since surging occurs withthe cessation of flow through the duct, or with reduction in the volumeof such flow appreciably below the-normal blower discharge volume, it issumcient toprovide disabling means which is automatically brought intooperation by the reduction or flow rate through the duct below apredetermined minimum value,

and this is conveniently accomplished by caus-' ing the disabling meansto. be effected by the decrease or pressure diflerential through theVenturi meter l5, or in the connections 23 and 21, below a predeterminedvalue, whereas under nor- During normal flow conditions through theduct.

II and Venturi meter l5, that is to say, when the valve 2 is opensufilciently to enable substantially all the normal blower dischargevolume of air to flow through it, the diiierence of pressure as betweenthe suction chamber 52 and the pressure chamber 53 urges the diaphragm5| and the valve 5 connected therewith upwardly, thereby closing thevent passage 50, and during such normal operation the surge relief valve3 operates in all respects similarly to the same valve in the simpleform shown in Figure 2. It can still be forced open by conduit pressureacting against the resistance of air trapped above it. Immeopened. Sincethis vent 50 opens to the sur-.

rounding atmosphere, there is no longer any entrapped elastic .airvolume within the chamber 33, and consequently no appreciable resistanceother than the very small weight of the valve 3 itself to resist openingof the surge relief valve under the influence of an increase inpressure, whether surge-induced or otherwise, within the duct II. Inconsequence the valve 3 immediately opens as much as necessary to ventthe portion of the air discharged by the blower under normal operatingconditions which cannot flow through valve 2 to the cabin, and, itsurging commences, relieves the peaks of such surges, and is app ciablymore sensitive and more apt to be in synchronism with the surge peaksthan the form of the valve shown in Figure 2. Furthermore, the

a rasm or temperature increase alone, or to both.

The form shown in Figure 4 is similar to that shown in Figure 3, thechief difierences in structure being that in Figure 4 the vent passage,controlled by the vent valve 5, is not directly between the interior ofthe casing 33 and the exterior, but is by way of and through the chamber53', beneath the diaphragm 5i, and thence to the atmosphere by way ofalways-open ports 50', which alone afford communication between thechamber 53' and a space which, for proper operation, should be at ahigher pressure than the chamber 52 (as the atmosphere). vThe creationof a pressure difference between the chambers 53 and 52, in Figure 3, isdependent upon the flow through the Venturi meter !5 creating such apressure difference, and this difference is reduced pro tanto, orbecomes zero, when flow through the Venturi meter is reducedcorrespondingly, or ceases. In the latter case, with the cabin at any,given pressure, the air pressure within the cabin will equalizethroughout the inflow duct, including the Venturi meter l5, as far asthe now closed valve 2. Pressur within the connections 2S and 2'! isthen equal, and it is equal in the two chambers 52 and 53. Its absolutevalue will be higher than the absolute pressure of the surroundingatmosphere, if the cabin is supercharged, but it is equal. Thus when theflow through venturi l5 ceases, or decreases to a value such that theresultant pressure difierential which such reduced flow creates ondiaphragm throat might not 'be greater than. the'atmospheric pressure,but merely not enough lower than atmospheric to create a pressuredifferential on diaphragm 5| suflicient to overcome the tension ofspring 55. As a result, the vent valve 5 always would stand open, sothat the form of Figure 4 can not be used for pressurecabin operation,at least, in such a system and arrangement as is shown.

The arrangement of Figure 4 is suitable, however, if the cabin is riotto be supercharged. At all altitudes, if the valve 2 is closed, thepressure within the chamber ,52 is equal to that within the chamber 53',and the spring force controls.

If the valve 2 is open, flow through the Venturi meter still creates aminus pressure through the connection 27, minus as related to cabinpressure, which in turn is the external atmospheric pressure, which isthe pressure withinthe chamber 53'. Thus wehave a minus pressure abovethe diaphragm 5i, and a plus pressure below it. which is theconditionrequired to close the vent valve 5, yet still substantialreduction of flow below normal, or cessation of flow, destroys thepressure difference required to overcome the tension of spring 55, andit opens the vent valve 5,,

' pressure relief valve, sudden, non-recurring-in- 5! is less than theforce of the spring 55, such diaphragm will be deflected by the spring,opening valve 5.

But if we were to connect the chamber 52 of the form of Figure 4,through .the connection 27, to the suction-producing throat of theVenturi meter l5 leading into a supercharged cabin, as we should have todo if the surge relief valve is still to be enabled to open under theinfluence of change in cabin 'air flow conditions, we might; andprobably would, find that, during normal flow conditions, withoutsurging, the vent valve 5 would be open, venting the chamber 33, andpermitting opening of the surge relief valve 3 under slight pressurewithin the duct ll. Such operation is not permissible. The reason for itis that, while the pressure through the Venturi throat is, with relationto the supercharged cabin pressure at one side of the throat and theblower pressure at the other side, a lower .or minus pressure, it isstill a plus pressure as related to some still lower pressure-that ofthe surrounding atmosphere, for instance. If, then, the pressure withinthe chamber 52, communicated through the connection 21, is a given pluspressure, as itcreases of pressure; that the device will operateautomatically with little 0r no attention,. once it has been initiallyinstalledand set; and that it will function automatically to prevent theoccurrence (or at least, the continuance) of pressure or temperatureswhich might be potentially dangerous, either to the duct system or todelicate materials which are in communication therewith and which aresensitive to high temperatures.

What we claim as ourinvention is: v -1. In a pneumatic system whichincludes a conduit wherein, under certain conditions, a

surging tendency arises, the conduit having an aperture, a surge reliefvalve cooperating with said aperture to close the latter, and formed as1 a piston, a chamber closely and slidably receiving said piston, tocontain therebetween an elastic air volume normally acting to resistopening of the surge relief valve at normal conduit pressures, butwhereby the surge relief valve may be opened in opposition to saidelastic air volume upon the occurrence of an overpowering surge peakwithin the conduit, the piston being pierced,

and'follow-up means disposed to cover the pierce in the piston in allitspositions, and movable in response to continuation of the surging, undersuch conditions to stabilize the surge relief valve in an open position.

- said aperture to close the latter, and formed as a piston, a chamberclosely and slidably receiving ,said piston, to contain therebetween anelastic air volume normally acting to resist opening of the surge reliefvalve at normal conduit pres.-

sures, but whereby the surge relief valve may be opened in opposition tosaid elastic air volume upon the occurrence of an overpowering surgepeak within the conduit, the piston 4 being pierced, follow-up meansdisposed to cover the pierce in the piston in all its positions, andthermostatic means in the conduit operatively connected to saidfollow-up means, to follow opening movement of the piston under theinfluence of rising temperature, pressure-induced, and therebyto holdthe surge relief valve open during the continuance of such temperaturconditions. V

3. In a pneumatic system which includes a conduit wherein, under certainconditions, a

nected to said vent valve, and normally operable,

under the influence of a pressure difference induced by flow through theconduit, to hold the vent valve closed, but operable automatically toopen the vent valve upon decrease of flow through the conduit reducingthe pressure difierence induced thereby below a predetermined value,whereby to destroy resistance of the elastic air volume within saidchamber to opening of the surge relief valve, the piston being pierced,a thermostat within the conduit movable in response to risingtemperature, pressure-induced,

and a follow-up means controlled by said thermostat to followpressure-induced opening'movement of the surge relief valve, and tendingthereby to close such pierce, thereby to hold the surge relief valve inan attained open position during the continuance of such temperature,conditions.

4. A relief valve device-for a blower discharge conduit whereinundercertain flow conditions a surging tendency arises, comprising avalve normally closing an aperture in such conduit, incapable of beingunseated by a gradual increase of pressure inthe conduit regardless ofits magnitude, but sensitive to uncover such aperture by a relativelyabrupt increase of pressure in the conduit though of relatively smallmagnitude, and means actuated by increase of temperature in the conduitto increase the sensitivity of said valve, whereby it will be openedby aless abrupt increase in pressure within the conduit.

conduit wherein, under certain conditions of reduced flow, a surgingtendency is produced. the conduit having a wastage aperture, a surgerelief valve cooperating with said aperture to normally close thelatter, and formed as a piston, a chamber slidably receiving saidpiston, to contain therebetween anelastic air volume, said piston beingconstructed to afford gradual pressureequalizing flow of air betweensaid chamber and the conduit, thus being incapable of being moved toopen the wastage aperture by a gradual increase of pressure in theconduit regardless of its magnitude, but movable to open the wastageaperture by a relatively abrupt increase of pressure in the conduit,though of relatively small magnitude, immediately following a suddendecrease in the velocity of air flow through the conduit, thereby toenable opening of the surge relief valve upon the occurrence of surgepeaks, and thermostatic means within the conduit operable to throttlethe pressure-equalizing flow of air between said chamber and the conduitand thereby to enable a less abrupt increase of pressure in the conduitto move said piston to open the wastage aperture.

'7. A wastage valve for use with a valve-seated vent aperture in apneumatic condit subject to surging, comprising a cylinder surroundingthe vent aperture, and itself vented, a piston slidably received in thecylinder and formed as a valve to close the vent aperture, being ofsmall mass,

, shiftable to restrict pressure-equalizing commu- 5. A relief valvedevice for -a blower discharge conduit wherein under certain flowconditions a surging tendency arises, comprising a valve normallyclosing an aperture in such conduit, difierential-pressure operated,valve moving means operable to move said valve to uncover such apertureby an abrupt increase of pressure in the abrupt increase in pressurewithin the conduit.

6. In a pneumatic system which includes nication through the pierce, andmeans sensitive to temperature rise in the conduit to move said membertoward pierce "restricting position.

8. In a pneumatic 'system which includes a conduit wherein at times asurging tendency of flow arises, a wastage aperture leading from theconduit, a cylinder over the conduit aperture and itself apertured tothe atmosphere at its inner 'end, a piston received in said cylinder andhaving valve means normally closing the cylinder aperture, and slidableoutward by direct pressure of surging flow in the conduit to open thecylinder aperture to saidconduit, air entrapped in the cylinder's outerend by said piston, during a, flow rate through said conduit greaterthan a predetermined value, damping such outward piston value, whilesaid piston is in aperture closing position, to vent to atmosphere theair entrapped within the cylinders outer end, thereby eliminating thedamping action on said piston while moving'outwardly during continuanceof such decreased flow rate through the conduit.

9. In a pneumatic system which includes a conduit. wherein at times asurging tendency of flow arises, a wastage aperture leading from theconduit, a cylinder over the conduit aperture and itself apertured tothe atmosphere at its inner end, a piston received in said cylinder,formed as an inwardly-seating valve normally closing the cylinderaperture and the conduit aperture, and slidable outwardby directpressure of surging flow in the conduit to open the cylinder aperture tosaid, conduit, air entrapped in the cylinder's outer end by said piston,during a flow rate mined value, damping such outward piston movement byits compression of such air, a vent passage for establishingcommunication between the cylinders outer end and the atmosphere, a ventvalve separate from and independent of said piston to closesaid ventpassage, vent valveclosing means operatively connected to said ventvalve,'

and operated to hold said vent valve closed by a pressure difierentialbetween points within said conduit created by a flow rate therethroughgreater than such predetermined value, regardless of simultaneoussimilar fluctuation in absolute pressure at such points, but renderedinoperative to hold the vent valve closed by a decreased pressuredifferential created by, a flow rate through said conduit less than suchpredetermined value, while said piston is in aperture closing position,and yieldable means opposing said vent valve closing-means and operableto open said vent valve positively when the vent valve closing means isthusrendered inoperative, to vent to atmosphere the air entrapped withinthe cylinders outer end, thereby eliminating the damping action on saidpiston while moving outwardly during continuance of such decreased flowrate through the conduit;

10. The combination oi' claim 9, wherein the vent valve closing meansincludes a casing divided by an imperforate flexible diaphragm into twoseparate chambers, and the vent valve is connected for movement withsaid diaphragm, and means in communication with the conduit operable totransmit diilerential pressures therein to the two chambers, forexerting a force on said diaphragm great enough to overcome theyieldable means and to hold the vent valve'closed through the conduitbelow such value decreasing by aflow rate through as conduit greaterthan such predetermjnedvalue exerting a force on said diaphragm greatenough to overcome the yieldable means and to hold the vent valveclosed,

the yieldable means operating to open the vent valve upon reduction ofsuch pressure dlflerence by decrease of flow through the conduit belowsuch predetermined value.

12. In a pneumatic system which includes a conduit wherein at times asurging tendency of flow arises, a wastage aperture leading from theconduit, a cylinder over the conduit aperture and itself apertured tothe atmosphere at its inner. end, a piston received in said cylinderhaving valve means normally closing the cylinder aperture, and slidableoutward by direct pressure of surging now in the conduit to open thecylinder aperture to said conduit, air entrapped in-the cylinders outerend by said piston, during a flow rate through said conduit greater thana predetermined value, damping such outward piston movement by itscompression'of such air, a vent passage for establishing communicationbetweenthe cylinderls outer end and the atmosphere, a

vent valve separate from andindependent of said piston to close saidvent passage, vent valve clos- I while the flow rate through the conduitis greater than such predetermined value, reduction of flow the force onsaid diaphragm suiflciently to enable opening'of the vent valve by theyieldable means.

11. The combination of claim 9 wherein the vent valve closing meansincludes a casing divided by an imperforate flexible diaphragm intotwonon-communicating chambers, and the vent valve 1 is connected formovement with-said diaphra m,

a Venturi meter in the conduit, a suction connection between the throatof the Venturi meter and one of said chambers, a pressure connectionbetween the other chamber and a space subjected to pressure during flowthrough the venturi, the

pressure difl'erence created in said two chambers mg means, including acasin an imperforate flexible diaphragm dividing said asing into twonon-communicating chambers, and connected for movementlwith said ventvalve, one of said chambers being in said vent passage between said ventvalve and the atmosphere, means responsive to a flow rate greater thansuch predetermined value to impose a suction on' the other chamberexerting a; force on said diaphragm great enough to hold said vent valveclosed, but rendered inoperative to hold the vent valve closed by adecreased suction-created by a flow rate through said-conduit less thansuch predetermined value, while said piston is in aperture plosingposition, and yieldable means opposing said vent valve 'clom' means, andoperable to open said vent valve pom-j tivelywhen the vent valve closingmeans is thus rendered inoperative. to vent to atmosphere through thechamber in the vent passage the air entrapped within the cylinders outerend, thereby eliminating the damping action on said piston while movingoutwardly during continuance oi said decreased flow through the conduit.

JAMES B. coorna.

NATHAN C. RICE.

through said conduit

